Safe and accurate diagnosis of chromosomal abnormalities is a major goal of prenatal screening. The assessment of aneuploidies such as trisomy 21 (Down's syndrome; DS) currently involves suggestive serum tests that are subsequently validated by invasive procedures such as amniocentesis or chorionic villus sampling. We have applied the tools of proteomic analysis to confirm the hypothesis that maternal serum markers for DS exist and can be used in the design of accurate and non-invasive tests. In our SBIR Phase-l studies, we identified specific differentially expressed protein biomarkers in maternal serum that were consistently characteristic of DS pregnancies. In this Phase-ll application, we propose to (1) verify the differential expression of the putative DS biomarker set in a larger cohort of DS and gestational age and sex-matched control samples derived from the FASTER NIH Trial database, and (2) develop a prototype MALDI-based high-throughput assay that will be validated in a blinded study employing the FASTER dataset supplemented with additional DS and control samples banked by ProeoGenix, Inc. The proposed studies extend our initial biodiscovery research and constitute the logical next step in the implementation of a proteomics-based analytical test that can be offered commercially, and which will replace current testing modalities.